1. Field of the Invention
The present invention relates to a discharge lamp energizing power supply device having a full-wave rectifier circuit for rectifying an AC voltage obtained from a commercial AC power supply system into a full-wave rectified waveform, a booster circuit for boosting the voltage of the full-wave rectified waveform, a boosted-voltage changing circuit for changing the boosted voltage output from the booster circuit, and a voltage lowering circuit for lowering an output voltage from the boosted-voltage changing circuit and outputting an activating output voltage for activating a discharge lamp to turn on the discharge lamp and an energizing output voltage for keeping the discharge lamp energized, and more particularly to a discharge lamp energizing power supply device for reducing a power loss for increased efficiency with respect to a wide range of power supply voltages and keeping a discharge lamp energized stably even when the discharge lamp is deteriorated.
2. Description of the Related Art
Heretofore, a discharge lamp energizing power supply device of the type described above (hereinafter referred to as “power supply device”) needs a large pulse current during a period of time after it is supplied with a lamp energizing signal until a discharge lamp to be energized enters an arc discharge phase because of the characteristics of low-voltage discharge lamps. The power supply device is required to boost a DC voltage obtained from a commercial AC power supply system to a voltage of several hundred volts (V), e.g., DC 360 V, or higher to cause an electric discharge in the discharge lamp. The power supply device employs a known booster chopper as an AC/DC converter capable of rectifying an AC voltage into a high DC voltage by way of full-wave rectification.
The booster chopper outputs a boosted voltage higher than the voltage that is required to energize the discharge lamp in order to improve the power factor to a higher value. Therefore, the power supply device employs a voltage lowering chopper comprising a DC/DC converter as a voltage lowering circuit. The voltage lowering chopper lowers the boosted voltage produced by the booster chopper to the voltage that is required to energize the discharge lamp. Consequently, if a voltage of DC 360 V is required to energize the discharge lamp, then a boosted voltage higher than DC 360 V is required. The boosted voltage produced by the booster chopper needs to be higher than the maximum peak value of an allowable voltage range in order to prevent a noise margin from being affected. Therefore, a high boosted voltage value is required from this standpoint.
Generally, a power supply device which employs a voltage of AC 200 V from a commercial power supply system needs to handle input voltages in an allowable voltage range from 180 V to 270 V.
If the boosted voltage is to be constant regardless of the wide power supply voltage range, then the voltage boosting ratio tends to increase greatly. When the input power supply voltage is low, the voltage boosting ratio is very high, resulting in an increase in the power consumption and heat loss.
Japanese laid-open patent publication No. 2001-52886 discloses an energizing device incorporating therein a power supply device which has a sufficient noise margin and comprises a booster chopper capable of reducing the power consumption and heat loss and a control function.
The energizing device disclosed in the above publication has a power supply voltage detecting means connected to the input of the booster chopper of a booster circuit and a plurality of boosted voltage detecting means connected to the output of the booster chopper. The energizing device also has a control means for switching between the boosted voltage detecting means based on the power supply voltage detected by the power supply voltage detecting means, and controlling the booster chopper at a certain output voltage value when a switched output of the booster chopper is confirmed by the boosted voltage detecting means. The boosted voltage value is switched based on the power supply voltage.
A basic arrangement of the above power supply device will be described below with reference to FIG. 1 of the accompanying drawings.
A power supply device shown in FIG. 1 comprises an AC/DC converter including full-wave rectifier circuit 2 for converting an input AC voltage E obtained from commercial AC power supply system 1 into a full-wave rectified waveform and booster circuit 11 for boosting a maximum rectified voltage value EO with a booster chopper and outputting the boosted voltage value, and a DC/DC converter including voltage lowering circuit 14 for lowering the boosted voltage and outputting the lowered voltage to keep discharge lamp 6 energized after discharge lamp 6 is turned on by an electric discharge therein.
Details of booster circuit 11 will be described below with reference to FIG. 2 of the accompanying drawings.
As shown in FIG. 2, booster circuit 11 cooperates with input voltage detecting circuit 31 and boosting control circuit 30 in making up the booster chopper. Booster circuit 11 has as its basic components switching device 21, choke coil 22, flywheel diode 23, and smoothing capacitor 24. The components of booster circuit 11 are arranged to produce at its output side an activating output voltage VO using an input voltage EO detected by input voltage detecting circuit 31 and an output voltage VO detected by output voltage detecting circuit 32.
The basic components and circuit arrangement of booster circuit 11 are well known in the art. Specifically, choke coil 22 and flywheel diode 23 are connected in series to each other from input to output terminals of booster circuit 11. Switching device 21 is connected to the junction between choke coil 22 and flywheel diode 23, and smoothing capacitor 24 is connected to the output terminal of flywheel diode 23 parallel to switching device 21. Technical details of booster circuit 11 will not be described below as they are of known nature.
Booster circuit 11 converts the input full-wave rectified voltage value EO into a DC voltage, boosts the DC voltage to the activating output voltage VO with an improved power factor, and outputs the activating output voltage VO to voltage lowering circuit 14 which comprises a voltage lowering chopper. Booster circuit 11 is included in power-factor improver 104.
Details of voltage lowering circuit 14 will be described below with reference to FIG. 3 of the accompanying drawings.
As shown in FIG. 3, voltage lowering circuit 14 cooperates with input voltage detecting circuit 51 and voltage lowering control circuit 50 in making up the voltage lowering chopper. Voltage lowering circuit 14 has as its basic components switching device 41, choke coil 42, flywheel diode 43, and smoothing capacitor 44. The components of voltage lowering circuit 14 are arranged to produce at its output side an energizing output voltage VL using an input voltage VO detected by input voltage detecting circuit 51 and an output voltage VL detected by output voltage detecting circuit 52.
The basic components and circuit arrangement of voltage lowering circuit 14 are well known in the art. Specifically, switching device 41 and choke coil 42 are connected in series to each other from input to output terminals of voltage lowering circuit 14. Flywheel diode 43 is connected to the junction between switching device 41 and choke coil 42, and smoothing capacitor 44 is connected to the output terminal of choke coil 42 parallel to flywheel diode 43. Technical details of voltage lowering circuit 14 will not be described below as they are of known nature.
In FIG. 1, energizing device 5 which includes voltage lowering circuit 14 turns on and off discharge lamp 6 in response to an energizing signal S that is input from outside of energizing device 5.
For turning on discharge lamp 6, energizing device 5 starts to operate with the energizing signal S. In response to the activating output voltage VO that is input from power-factor improver 104, the voltage lowering chopper of voltage lowering circuit 14 of the non-insulating type that is incorporated in energizing device 5 applies an ignition pulse to produce and output the energizing output voltage VL. Discharge lamp 6, which may be a high-voltage mercury lamp, a metal halide lamp, or the like, develops an arc discharge therein in response to the energizing output voltage VL, and maintains the arc discharge to remain continuously energized.
Rectified voltage detecting circuit 3 is connected to the output of full-wave rectifier circuit 2 for detecting its output voltage. Drive voltage detecting circuit 13 is disposed at the output of power-factor improver 104 for detecting its output voltage. Energizing voltage detecting circuit 15 is disposed at the output of energizing device 5 for detecting its output voltage. Booster circuit 11 and voltage lowering circuit 14 have their respective boosting and voltage lowering actions stabilized using their detected input and output voltages.
The drive voltage VO which is an output of power-factor improver 104 that is supplied with the commercial AC voltage is required, due to the boosting action, to have a voltage value which is equal to or greater than the rectified voltage value EO of the full-wave rectified waveform and has a sufficient voltage boosting ratio for obtaining a high power factor.
Power-factor improver 104 has a loss which is generally a main loss in the booster chopper. The loss caused by power-factor improver 104 is predominantly provided by a loss caused by switching device 21 of booster circuit 11. This loss is proportional to the drive voltage VO output by power-factor improver 104. Therefore, power-factor improver 104 is of higher efficiency as the drive voltage VO output thereby is lower, i.e., as the voltage boosting ratio is smaller.
Energizing device 5 has a loss which is generally a main loss in the voltage lowering chopper. The loss caused by energizing device 5 is predominantly provided by losses caused by switching device 41 and flywheel diode 43 of voltage lowering circuit 14. Of these losses, the loss caused by flywheel diode 43 that operates upon turn-offs is more predominant. This loss is proportional to an input voltage applied to energizing device 5, i.e., the drive voltage VO which is an output voltage of power-factor improver 104. Therefore, energizing device 5 has its efficiency made higher by lowering the drive voltage VO output by power-factor improver 104.
As described above, the total loss caused by power-factor improver 104 and energizing device 5 in the illustrated conventional circuit arrangement is maximum when a low voltage that requires a large voltage boosting ratio is input to power-factor improver 104. Consequently, power supply heat radiation requirements have to be designed in view of the loss caused when a low voltage is input.
According to the invention disclosed in Japanese laid-open patent publication No. 2001-52886, in order to reduce power consumption and heat loss in the power supply device which handles a wide range of DC power supply voltages, a control circuit switches between boosted voltages of the booster chopper based on the DC input voltage EO obtained from the commercial AC power supply system, and outputs a lower boosted voltage.
Specifically, as shown in FIG. 1, control device 107 is supplied with the maximum rectified voltage EO detected by rectified voltage detecting circuit 3 and obtained from the full-wave rectified output from the commercial AC voltage E, operates boosted output switching circuit 112 connected to the output of booster circuit 11 based on the rectified voltage EO to produce a lower boosted drive voltage VO. Control device 107 operates boosted output switching circuit 112 to switch between two drive voltages, i.e., higher and lower drive voltages.
Operation of control circuit 107 will be described below with reference to FIG. 4 of the accompanying drawings together with FIG. 1.
When the power supply device receives the AC voltage E obtained from commercial AC power supply system 1, full-wave rectifier circuit 2 converts the AC voltage E into the maximum rectified voltage EO.
Rectified voltage detecting circuit 3 detects a measured value of the rectified voltage EO applied thereto in step S91. Control device 107 determines whether the measured value is in a predetermined range, e.g., a range from 180 V to 270 V, or not in step S92. If it is confirmed that the measured value is not in the predetermined range in step S92, then control device 107 performs a process for indicating a power supply input failure to the user and stopping its function in step S93.
If it is confirmed that the measured value is in the predetermined range in step S92, then control device 107 determines whether or not the measured value is equal to or smaller than a preset value, e.g., 200 V, or not in step S94. If it is confirmed that the measured value is equal to or smaller than the preset value in step S94, then control device 107 switches boosted output switching circuit 112 to the higher boosted voltage in step S95 to cause boosted output switching circuit 112 to output the higher output voltage. The output voltage is measured by drive voltage detecting circuit 13 as the drive voltage value VO in step S96. Thereafter, control device 107 determines whether or not the drive voltage value VO is a predetermined value of 200 V or not in step S97.
If it is confirmed that the measured value is in excess of the preset value in step S94, then control device 107 switches boosted output switching circuit 112 to the lower boosted voltage in step S99 to cause boosted output switching circuit 112 to output the lower output voltage. The output voltage is measured by drive voltage detecting circuit 13 as the drive voltage value VO in step S96. Thereafter, control device 107 determines whether or not the drive voltage value VO is the predetermined value of 200 V or not in step S97.
If it is confirmed that the drive voltage value VO is the predetermined value of 200 V in step S97, then control device 107 performs a control process to stabilize the confirmed drive voltage value VO in step S98. If it is confirmed that the drive voltage value VO is not the predetermined value of 200 V in step S97, then control goes back to step S93 in which control device 107 performs the process for indicating the power supply input failure to the user and stopping its function.
With power-factor improver 104, when the power supply voltage E is low, the output voltage of boosted output switching circuit 112 is high, and when the power supply Voltage E is high, the output voltage of boosted output switching circuit 112 is low. As a result, when the power supply Voltage E is low, the boosted value is held to a low level thereby to reduce power consumption and heat loss. When the power supply Voltage E is high, the boosted value is increased to output a drive output with a sufficient noise margin.
However, the conventional discharge lamp energizing power supply device is not suitable for use as a general-purpose power supply device which operates efficiently in a wider range of power supply voltages, e.g., a range from AC 100 V that is used in Japan to AC 240 V that is used in Europe.
The first reason is that with the above conventional arrangement, the rectified voltage value EO obtained from the power supply voltage E by way of full-wave rectification is in a given range only and can be switched to two values, and the booster circuit fails to operate when the power supply voltage is generated in excess of a predetermined voltage value.
The second reason is that the voltage lowering circuit is unable to operate when the energizing output voltage required by the discharge lamp exceeds an energizing output voltage output as an activating output voltage for reasons on the output side, e.g., a characteristic deterioration of the discharge lamp.